1. Field of Invention
The present invention relates to an improved gamma-ray spectrometer. More specifically, the present invention relates to a gamma-ray spectrometer incorporating a method of improving the energy resolution of detectors whose energy resolution is degraded because of charge carrier trapping.
2. Description of the Related Art
The germanium detector is the most commonly used high-resolution gamma-ray detector. When the germanium detector absorbs a gamma-ray photon, free electrons and holes are produced. The number of electrons and holes produced is proportional to the gamma-ray energy. The associated electronics collects the electrons and holes producing a signal proportional to the gamma-ray energy. The energy spectrum of the system is a histogram of the number of measured events versus the recorded energy. The width of the line in the energy spectrum caused by a mono-energetic gamma-ray source is called the energy resolution of the system. The width of the line is usually measured at the point where the number of counts is half of the maximum in the peak and is referred to as the Full Width at Half Maximum (FWHM).
Only the electronic noise and the statistical variation in the collected charge would limit the energy resolution of a perfect detector. In addition to electronic noise and statistical variations, the energy resolution of real detectors is degraded when some of the free charge carriers are trapped before reaching the collecting electrodes. The fraction of the charge signal that is lost depends on the point of interaction of the gamma-ray inside the germanium crystal and thus varies from event to event producing an increase in the FWHM.
U.S. Pat. No. 4,937,452, entitled “Charge Trapping Correction in Photon Detector Systems,” issued to Michael L. Simpson, et al., on Jun. 26, 1990 shows an analog spectrometer that corrects for the trapped charge and improves the energy resolution. Although the energy resolution is improved, the Simpson device requires the manual adjustment of two independent parameters to match the specific detector being used.